There is a rule in the motion-picture industry called the 180-rule, this is a rule followed for spatial-continuity in order not to confuse the audience as to the position of the subjects in space that the audience are seeing on the screen. The idea is simple, when photographing two subjects in a scene any other shot must match the positioning of the subjects from the first establishing-shot, otherwise we will have confusion and what will appear to be mistakes through mis-matching of images.
In this shot from my last assignment (above) the two characters sit at a table, the female to the left, male to he right, any new shot taken to cover this scene must make sense therefor, any new camera-angle employed must keep the female to the left and the male to the right otherwise the audience will believe that the characters have either physicly changed position or it must be another time, another day, or more likely, the film-maker has made a very bad blunder.
Here is an example of the 180 rule in action, above we have the establishing long-shot of the couple sitting at the table in conversation, followed by the two smaller images of the over-the-shoulder, medium-close-up shots of the female and male, notice how the female maintains her position to the left of the screen and the male to the right.
The Axis of Action.
This is commonly known as the action-axis, or axis-of-action, an imaginary line has been drawn through the female and the male and the camera has remained on the nearside of this imaginary line.